Paleomagnetic evidence for the existence of the geomagnetic field 3.5 Ga ago
Article first published online: 20 SEP 2012
Copyright 1980 by the American Geophysical Union.
Journal of Geophysical Research: Solid Earth (1978–2012)
Volume 85, Issue B7, pages 3523–3528, 10 July 1980
How to Cite
1980), Paleomagnetic evidence for the existence of the geomagnetic field 3.5 Ga ago, J. Geophys. Res., 85(B7), 3523–3528, doi:10.1029/JB085iB07p03523., and (
- Issue published online: 20 SEP 2012
- Article first published online: 20 SEP 2012
- Manuscript Accepted: 12 DEC 1979
- Manuscript Received: 26 JUN 1979
A paleomagnetic study has been made of the red dacite and pillow basalt of the Duffer Formation of the Pilbara craton, Australia. The dacite is currently the oldest dated rock unit in Australia, having a zircon U-Pb age of 3452±16 Ma. Vector analysis of alternating field and thermal demagnetization results yield three components of magnetization. The high-temperature, high-coercivity hematite (H) component in the red dacite appears to be postfolding in age, as does a low-temperature, low-coercivity (L) component observed in the pillow basalt. However, an intermediate-temperature, intermediate-coercivity magnetite (M) component observed in both the pillow basalt (five sites) and the red dacite (six sites) is clearly prefolding in age and thus older than 3.0 Ga. This M component appears to be the oldest magnetization yet recorded in paleomagnetic studies and yields a paleomagnetic pole, probably original, at 43.9°N, 86.3°E (A95 = 7.2°). A tentative Archean apparent polar wander path for Australia suggests that the L and H components are also ancient magnetizations, probably 3.0 and 2.6 Ga old, respectively. The primary M component establishes the existence of the geomagnetic field at least 3.5 Ga ago.